Tone-control agents for silver halide emulsions



Patented July 8, 1947 TONE-CONTROL AGENTS FOR SILVER HALIDE EMULSIONSDouglas James Fry and James Douglas Brooks, Ilford, England, assignorsto Ilford Limited, Ilford, England, a British company No Drawing.Application December 13, 1944, Se-

rial N0. 568,066. 3, 1944 18 Claims. 1

This invention relates to the production of photographic light-sensitiveemulsions and to the production of photographic light-sensitive elementsincluding layers of such emulsions.

It is Well known that photographic emulsions consisting predominantly ofsilver chloride, unless steps are taken to prevent it, yield ondevelopment images which tend to be greenish-black or brownish-blackrather than a good neutral black. This phenomenon also occurs to someextent in the case of emulsions consisting predominantly of silverbromide, especially fine grain emulsions of this type, but whereas it isknown that by the addition of certain compounds it is possible tocorrect the image colour of silver chloride emulsions so that the imagesobtained are more of a bluish black, the compounds added to suchemulsions to produce this correction usually have little or no effect onsilver bromide emulsions.

According to the present invention the colour of the developed image inphotographic silver halide emulsions, including silver bromideemulsions, is improved by applying to the emulsion, at a stage not laterthan its development, a small quantity of a compound of the generalformula:

wherein R1 is a hydrogen atom or a substituent group, e. g., alkyl (forinstance methyl, ethyl, propyl or higher alkyl) aryl (for instancephenyl or naphthyl), aralkyl (for instance benzyl or naphthyl methyl),amino, hydrocarbon-oxy (for instance alkoxy) hydrocarbon thiol (forinstance alkyl thiol) alicyclic (for instance cyclopentyl or cyclohexyl)or heterocyclic (for instance furoyl, nicotinoyl, picolinoyl, coumarylor indolyl) or a substituted group of any of these types, and R2 is anamino, hydrocarbon-oxy (for instance alkoxy) hydrocarbon thiol (forinstance alkyl thiol) or a substituted group of any of these types.

Some typical examples of compounds suitable for use are:

In Great Britain February (i) Acetyl-4 4-diethyl-thiosemicarbazideCH3.CO.NH.NH.CS.N(C2H5) 2 (7') Furoyl-dithiocarbazinic acid methyl ester(Cd-I30) .CO.NH.NH.CS.SCH3

(k) Cyclohexyl carbonyl-dithiocarbazinic acid methyl ester (l)Butyryl-dithiocarbazinic acid methyl ester C3H7.CO.NH.NH.CS.SCH3

The preparations of compounds (a), (b), (d) and (e) are described inBeilsteins Handbuch der Organische Chemie, 4th edition, compounds (0)and (1) may be prepared by treating methyl dithiocarbazinate with theappropriate acetic or propionic anhydride or with the appropriate acetylor propionyl chloride in pyridine, and compound (g) may be prepared bytreating methyl dithiocarbazinate with ethyl chloroformate in pyridine.Compound (h) may be prepared by reacting benzyl dithiocarbazinate withacetic anhydride or acetyl chloride in pyridine and compound (i) may beprepared by the analogous method described in Journal fiir PraktischeChemie, volume 159 at pages 189- 92 (1941). Compound (:i) may beprepared by reacting methyl dithiocarbazinate with furoic anhydride orfuroyl chloride, and (k) by reacting methyl dithiocarbazinate withcyclohexane carboxylic acid anhydride or chloride. Compound (Z) may beprepared by reacting methyl dithiocarbazinate with butyric anhydride orbutyryl chloride in pyridine. Other compounds included within the scopeof this invention may be made by analogous methods using the appropriatestarting materials.

The compounds are preferably applied to the emulsions by actualinclusionin the emulsion during its manufacture, or by inclusion in thedeveloping solution with which the photographic element carrying theemulsion is treated. However, they may be included instead in a layer ofthe photographic element coated adjacent to the emulsion layer, e. g.,in a subcoat or supercoat layer, or may be applied to the emulsion fromsolution prior to development, The invention is of greatest importancein connection with the application of the compounds to fine grain silveriodobromide emulsions.

As indicated above, the compounds should be used in small quantitiesonly. In the case where the compounds are included in the emulsion or inan adjacent layer a proportion of the order of 50 cos. of a 1% solutionof the compound in ethyl alcohol, or other suitable solvent, per litreof emulsion or other coating solution, is generally satisfactory, thoughthe optimum proportion will depend on the nature of the precise compoundemployed and on the nature of the emulsion or other coating solution inwhich it is incorporated. Thus a wide range of proportions is practical,e. g., from 1 to cos. of a 1% solution per litre 3 of emulsion or othercoating solution. When added to the developer solution or applied fromsolution before development, the compound may conveniently be present ina proportion of the order of 1 part in 5,000-20,00G of such solution.

Smaller proportions than these are operative, but

usually do not have as large effect as is desired.

Higher proportions may be used, but are usually uneconomic. Thecompounds may be used either as the free compounds or as their metalsalts, e. g. their alkali metal salts or silver salts.

All the compounds (a) to (I) listed above improve the image colour in asilver bromide emulsion or silver iodobromide emulsion when used in anyof the ways indicated above, making the resulting developed image a goodblack which may even tend towards a bluish tint. Compounds (f) and (9)give particularly good results. When the compounds are included insilver chloride emulsions, or added to the developer for such emulsionsor otherwise applied to such emulsions at a stage not later thandevelopment, they tend to change the image colour from a greenish orbrownish black to a bluish-black. The compounds present the furtheradvantage that they do not cause any serious loss in the speed of theemulsions in which they are incorporated.

An approximate measure of the improvement in the tone of the developedemulsion can be obtained by the following method. The silver density ofthe developed emulsion is measured first through an orange filter whichtransmits freely from 5900 A. to the infra-red but absorbs light oflower wavelengths (D0) and then through a blue filter which transmitslight between 3700 A. and 5100 A. and absorbs light. of otherwavelengths (DE).

A positive figure for T indicates a warm tone and a negative figure acold tone. In the following table the results obtained With certain. ofthe above compounds are listed, as obtained by adding the compounds to afine-grain gelatin silver iodobromide emulsion.

Table Quantity of 1% solution per liter'of emulsion Code Letter StandardR1-CO-NI-I--NHC(=S) R2 where R1 is selected from the group consisting of4 the hydrogen atom and alkyl, aryl, aralkyl, amino, hydrocarbon-oxy,hydrocarbon-thiol, alicyclic and heterocyclic groups, and R2 is selectedfrom the group consisting of amino, hydrocarbon-oxy andhydrocarbon-thiol groups.

2. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesapplying to the emulsion, at a stage not later than its development, asmall quantity of a compound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-oxy, hydrocarbon-thiol,,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-.oxy and hydrocarbon-thiol groups.

3. .A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesapplying to the emulsion/at a stage not later than its development, asmall quantity of a compound'of the general formula:

Where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

4. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesincluding in the emulsion during its manufacture a small quantity of acompound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, hydrocarbon-thiol, alicyclic and. heterocyclicgroups, and R2 is selected from the group consisting of amino,hydrocarbon-oxy and hydrocarbon-thiol groups.

5,. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesincluding in the emulsion during its manufacture a small quantity of acompound of the general formula.

where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

6. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesincluding in a layer coated adjacent to the emulsion a small quantity ofa compoundof the general formula:

Where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-oxy, 'hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

7. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide" emulsion which comprisesincluding in a layer coated adjacent to the emulsion a small quantity ofa compound of the general formula:

where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

8. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesdeveloping the emulsion with a photographic de- Veloper solutioncontaining a small quantity of a compound of the general formula:

where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

10. A process of improving the colour of the developed image in aphotographic fine grain silver iodobromide emulsion which comprisesincluding in the emulsion during its manufacture a small quantity of asilver salt of a compound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-oxy, hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

11. A photographic silver halide emulsion containing a small quantity ofa compound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-oxy, hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

12. A photographic fine grain silver iodobromid emulsion containing asmall quantity of a compound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-oxy, hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

13. A photographic fine grain silver iodobromide emulsion containing asmall quantity of a compound of the general formula:

where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

14. A photographic element containing a layer of photographic fine grainsilver iodobromide emulsion containing a small quantity of a compound ofthe general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-0X3, hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

15. A photographic element containing a layer of a photographic finegrain silver iodobromide emulsion and, adjacent thereto, a layercontaining a small quantity of a compound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-0x5, hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

16. A photographic element containing a layer of a photographic finegrain silver iodobromide emulsion and, adjacent thereto, a layercontaining a small quantity of a compound of the general formula:

where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

17. A photographic developing solution which includes, in addition tothe essential reagents for developin a silver image in a photographicsilver halide emulsion, a photographic developing agent and a smallquantity of a compound of the general formula:

where R1 is selected from the group consisting of the hydrogen atom andalkyl, aryl, aralkyl, amino, hydrocarbon-oxy, hydrocarbon-thiol,alicyclic and heterocyclic groups, and R2 is selected from the groupconsisting of amino, hydrocarbon-oxy and hydrocarbon-thiol groups.

18. A photographic developing solution which includes, in addition tothe essential reagents for developing a silver image in a photographicsilver halid emulsion, a photographic developing agent and a smallquantity of a compound of the general formula:

where R1 is a lower alkyl group and R2 is a lower alkyl thiol group.

DOUGLAS JAMES FRY. JAMES DOUGLAS BROOKS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,623,499 Sheppard et al Apr. 5,1927 2,124,159 Weyde July 19, 1938 2,298,093 Dersch et al Oct. 6, 19422,346,065 Carroll. et al Apr. 4, 1944 2,266,442 Schinzel Dec. 16, 19412,276,254 Schinzel Mar. 10, 1942 2,286,662 Weyde June 16, 1942 2,309,492Albers et a1 Jan. 26, 1943 2,311,098 Swan et a1 Feb. 16, 1943 OTHERREFERENCES Ser. No. 394,290, Bruylants et al., A. P. C. publ. May 4,1943.

